If you are looking for a solution which is independent of Gnome/KDE/Fluxbox or any Desktop Environment or Window Manager, try the following X Window System command. I need this because my Unity desktop is not loading (but X works fine), therefore there is no logout button.
Using the command line
You can type the following command to enable Zapping immediately.
setxkbmap -option terminate:ctrl_alt_bksp
If you're happy with the new
behaviour you can add that command to your
~/.xinitrc in order to make
the change permanent.
Also, according to the Ubuntu 10.04 LTS (Lucid Lynx), this has replaced the old
DontZap feature from older versions of the X Window System.
In addition, the Ctrl-Alt-Backspace option is now configured as an X
keymap (XKB) option, replacing the X server "DontZap" option and
allowing per-user configuration of this setting.
This is explained further in the Xorg X11R7.5 Release Notes which, among other details, say:
Users who wish to have this functionality available by default may
enable it via the XKB configuration option “terminate:ctrl_alt_bksp”.